1. Field of the Invention
The present invention relates to an exciting method for an elastic vibration member and a vibratory driving device.
2. Description of the Related Art
In the past proposed is an exciting method for an elastic vibration member in a vibratory driving device for linear or rotational motion.
For example, a first technique in the related art mentioned below is proposed. This technique includes an elastic vibration member, a drive member having at least two electrodes and an electro-mechanical energy transducer for exciting the elastic vibration member by applying drive voltages having the same frequency and two phases to these two electrodes, and a driven member kept in contact with the elastic vibration member. The drive member forms a first bending vibration mode by the input of the drive voltages having the same phase, and also forms a second bending vibration mode by the input of the drive voltages having opposite phases. By the combination of these two bending vibration modes, a circular or elliptical motion is produced in the elastic vibration member (see Japanese Patent Laid-open No. 2004-320846 referred to as Patent Document 1).
A second technique in the related art mentioned below is also proposed. This technique includes a square bar-shaped elastic base, a plurality of drive elements projecting from one side surface of the base at given positions, and an elastic vibration member connected to the base. By applying an alternating voltage to the base, bending resonance and longitudinal resonance are simultaneously produced in the base. By the combination of these bending and longitudinal vibration modes, a circular or elliptical motion is produced in the elastic vibration member (see Japanese Patent Publication No. 6-106028 referred to as Patent Document 2).
However, according to Patent Document 1, two bending vibration modes are combined so as to excite the elastic vibration member in a circular or elliptical motion.
Usually, the resonant frequencies in the two bending vibration modes are not equal to each other. Further, it is not ensured that the frequency ranges of these two bending vibration modes are adjacent to each other. To make the resonant frequencies in the two bending vibration modes equal to each other, adjustment (degeneration) of the size, shape, thickness, etc. of the elastic vibration member may be required, causing a limitation to the shape of the elastic vibration member and a difficulty of design.
In Patent Document 2, the bending vibration mode and the longitudinal vibration mode are combined. Accordingly, the use of the longitudinal vibration mode (vertical vibration) generally causes an increase in resonant frequency, which is impractical. Further, when the longitudinal size of the elastic vibration member is reduced, a further increase in resonant frequency is undesirably invited.
Moreover, both in Patent Document 1 and 2, a circular or elliptical motion as a driving force can be produced by combining the two vibration modes, or exciting the two vibration modes. Accordingly, precise control of the driving frequency and a limitation to the driving frequency are necessary. Further, a limitation to the shape and size of the elastic vibration member and a dimensional accuracy in working the elastic vibration member are necessary for the excitation of the two vibration modes at near frequencies, causing an increase in cost.